The present disclosure relates to an organic electroluminescence (EL) device suitable for a device including a resonator structure and a display unit including the same.
The organic EL device in which electroluminescence of an organic material is used has been already applied to an organic EL display unit as a light emitting device capable of realizing high luminance light emission by low voltage direct current drive. The organic EL device has, for example, a structure in which a lower electrode, an organic layer including a light emitting layer, and an upper electrode are sequentially layered over a substrate. Light generated in the light emitting layer is extracted from one of the lower electrode side and the upper electrode side or both sides. In the case where the light is extracted from the upper electrode, the upper electrode is made of, for example, a transparent conductive film. As a material of the transparent conductive film, for example, a metal oxide conductive material such as an oxide of indium and tin (ITO) and an oxide of indium and zinc (IZO) is used.
However, in the case where the transparent conductive material composed of the metal oxide is used, device characteristics are lowered due to damage at the time of sputtering deposition. Further, a sputtering film is strongly characterized by intruding into and adhering to a projection and a defect section of a deposition face. In addition, in order to express the electric conductivity of the metal oxide, the film thickness thereof should be about 15 nm or more. Thus, there is a high possibility that the metal oxide conductive material adheres to a foreign matter or a defect on the lower electrode or a defect section of the organic film, and short circuit between the upper electrode and the lower electrode is generated.
As a material of the upper electrode, a conductive film made of a metal film is also used. For example, in Japanese Unexamined Patent Application Publication No. 2004-164890, a description is given that an electron injection metal having a refractive index of 1 or less and an extinction coefficient of 0.5 or more is preferable as a material of the metal film in order to decrease absorption loss. For example, Japanese Unexamined Patent Application Publication No. 2004-164890 exemplifies a simple body or an alloy of aluminum, magnesium, calcium, sodium and the like.
The metal film has a thickness of about 10 nm, and functions as an electrode. The film thickness of the metal film necessary for expressing electric conductivity is small. Thus, there is a small possibility that short circuit is generated in a foreign matter or a defect on the lower electrode or a defect section of the organic film. Further, in the case where the metal film is deposited by vacuum evaporation method under high vacuum by using resistance heating, evaporation particle scattering caused by collision with gas molecules is hardly generated, and there is a small possibility that the conductive material intrudes into a foreign matter or a defect on the lower electrode or a defect section of the organic film.
However, there has been a disadvantage that the electric conductivity of the foregoing metal film is lowered by thinning the metal film. In the case of an alloy of magnesium and silver (Mg—Ag alloy), high electric conductivity is retained even if the film is thinned, but thinning limit has been above 6 nm. That is, in the past, there has been no known successful example that electric conductivity is retained to the degree that an organic EL device is able to be sufficiently driven with the use of a metal film having a thickness of 6 nm or less.
For example, in Japanese Unexamined Patent Application Publication No. 8-185984, a description is given that an upper electrode is made of an oxide conductive material, and a transparent Mg—Ag alloy film having a thickness of 2 nm is provided between an organic layer and the upper electrode in order to improve electron injection characteristics. The Mg—Ag alloy film does not have a function as an electrode, and has only a function as an electron injection layer. The oxide conductive material is responsible for electric conductivity.
Therefore, it is desirable to provide an organic electroluminescence device in which an upper electrode is made of a metal film, and the thickness of the metal film is able to be thinned down to 6 nm or less while electric conductivity of the metal film is retained, and a display unit including the same.